Conventionally, a rotation angle of a motor is detected by a magnetic sensor. For example, in the magnetic sensor disclosed in a patent document, Japanese Patent Laid-Open No. 2012-39737 (patent document 1), based on an assumption of musing two pairs of conductive wires, the corresponding phases are arranged to be point-symmetric to the magnetic sensor, which cancels a spill magnetic flux caused by an electric current flowing in the conductive wire, for the improvement of the detection accuracy of the rotation angle.
However, according to the patent document 1, an error of the detection angle is caused due to an assembly error of the magnet that rotates together with the shaft, the magnetic sensor, and the conductive wire (i.e., the position and/or the angle of those components shifted from an intended one). Further, when the conductive wires cannot be positioned as point-symmetric with each other due to a restriction of a manufacturing process or the like, the magnetic flux generated by the electric current flowing in the wire causes an error of the detected rotation angle.